In most machinery, the prime mover is separate from the ultimate device to be driven and, consequently, an interconnecting drive mechanism is employed. In some cases, belts are employed. Historically, belt drives started with flat belts. Belting with a circular section is often employed for low power applications. The low power applications were such that the belt of circular section could be cut from a single thickness of leather. As synthetic material was developed, both flat and round belts continued in use. However, the V-belt was developed wherein the force normal to the surface was greater than the radial belt force to result in a high friction installation without great belt tension. Round belts were sometimes used in V-belt sheaves where they were axially constrained. The round belts were also used in belt drive applications wherein the sheave was in half circular section with a belt groove equal to the round belt dimension. In such cases, the belt is axially constrained. The axial constraint of resilient elastomeric rings is illustrated in Davy U.S. Pat. No. 607,986 and Hamilton U.S. Pat. No. 3,094,006. The teaching in belt drives has been to axially constrain the belt.
A particular example of an apparatus in which the friction drive mechanism of this invention can be installed is a movie film transport system. A commercially available 35-millimeter movie film transport system operates with a large disc rotating on a vertical axis. In such an orientation, a long strip of film can be wound to present a long (for example, five hours) viewing program. In the takeup of film, the actual rotative speed of the takeup roller is controlled by the rate of supply of film from the projector. As the film winds, its winding diameter increases so that slower rotation gives constant peripheral winding speed. A friction drive is employed wherein a flat, resilient elastomeric tire is resiliently engaged on a drive wheel and is frictionally engaged against the bottom of the large platter which is the takeup reel. The problem with these tires is that there is a great deal of wear, which makes for a short life of the drive mechanism, but which also puts a lot of dust into the air. In a movie projection system, dust is objectionable and, as a result, dust in the area is to be avoided. An improvement is needed in such a system.